[Scanning electron microscopic observations of ookinete formation of Plasmodium yoelii yoelii in vitro]

The ookinete formation and mature ookinete of Plasmodium yoelii yoelii were described. During the development from zygote to ookinete, at first a finger-shaped or a stick-shaped projection protruded from one side of zygote. The anterior end of the projection assumed a truncated cone shape. Following enlargement of the projection, the body of zygote gradually wrinkled and shrank and became smaller. An annular structure developed between the newly formed ookinete and the remaining body of zygote, which ultimately separated from the ookinete. The ookinete was banana-shaped. The surface of mature ookinetes was smooth. On the tip there was an apical complex showing truncated cone shape. Behind the apical end there were a few pellicular folds. Through the course of development of the ookinete the parasite constantly showed obvious movement. As the parasites protruding forward, longitudinal and spiral wrinkles appeared on their body surface.